Free Fall & Projectiles 1


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Free Fall & Projectiles 1

  1. 1. Exploring Free Fall… <ul><li>Sir Isaac Newton was one of the revolutionary genius’s </li></ul><ul><li>who discovered and experimented with the laws of </li></ul><ul><li>motion. Often heard in today’s culture, Newton was </li></ul><ul><li>accredited with noticing the pattern of motion of an </li></ul><ul><li>apple falling from a tree, and onto the ground. A </li></ul><ul><li>simple everyday fruit, or a promising example of what </li></ul><ul><li>was to be found about gravity and physics as a whole? </li></ul><ul><li>After many experiments, Newton realized that gravity </li></ul><ul><li>was the force which was making the apple fall from the </li></ul><ul><li>tree to the Ground. </li></ul>
  2. 2. The 101 on Gravity… <ul><li>Sure everybody has heard of gravity at one time or another, </li></ul><ul><li>but what is gravity? Well gravity is the force of attraction by </li></ul><ul><li>which any objects tend to fall toward to the center of Earth. </li></ul><ul><li>Haven’t you ever heard the expression “the gravity of a </li></ul><ul><li>situation”? That simply means the seriousness or the </li></ul><ul><li>weight of the problem. Gravity causes us humans to stay </li></ul><ul><li>down on Earth’s surface and increase our weight. The </li></ul><ul><li>force of gravity is 9.81 meters per second (squared). This </li></ul><ul><li>stays true to whether you are talking about the force of </li></ul><ul><li>gravity on a mouse or an elephant. </li></ul>
  3. 4. A Common Question… <ul><li>So let’s say that you drop a rock out of an air </li></ul><ul><li>balloon. Will the speed of the falling rock remain at </li></ul><ul><li>9.81 m/s^2 the entire trip down, or will it increase? </li></ul><ul><li>Well think about it; if you caught a rock that was </li></ul><ul><li>dropped 2 meters above your head, you could do it </li></ul><ul><li>with ease, however if you were to catch a rock </li></ul><ul><li>dropped from 200 meters above you head, I’m </li></ul><ul><li>pretty sure it would hurt your hand thanks to the </li></ul><ul><li>speed of the falling rock. This obviously shows that </li></ul><ul><li>the speed of the rock does increase as it travels a </li></ul><ul><li>farther distance. </li></ul>
  4. 5. 50 5 40 4 30 3 20 2 10 1 0 0 Instantaneous Speed (m/s) Elapsed Time (seconds)
  5. 6. Acceleration… <ul><li>Acceleration is the rate at which the </li></ul><ul><li>velocity is changing. It is often </li></ul><ul><li>expressed as acceleration= change in </li></ul><ul><li>velocity/ time interval. The acceleration </li></ul><ul><li>of the object from the last chart was 10 </li></ul><ul><li>m/s^2. This was found because </li></ul><ul><li>acceleration= change in speed/ time interval= </li></ul><ul><li>10 m/s / 1 second = 10 m/s^2. </li></ul>
  6. 7. Practice Question… <ul><li>Suppose a car moving in a straight line </li></ul><ul><li>steadily increases it’s speed each </li></ul><ul><li>second, first from 35 to 40 km/h, the from </li></ul><ul><li>40 to 45 km/h, then 45 to 50 km/h. What </li></ul><ul><li>is it’s acceleration? </li></ul><ul><li>Answer: 5km/h </li></ul>
  7. 8. So What Does That Mean? <ul><li>This car is traveling at 60 miles per hour. Sure if they are on a </li></ul><ul><li>highway it mean they are probably going about the speed limit; but </li></ul><ul><li>what does it REALLY mean? It means that if that person travels </li></ul><ul><li>for one hour they go exactly 60 miles. Sure that’s really easy, but </li></ul><ul><li>many people think of speed and acceleration as one, but they are </li></ul><ul><li>not. If that same person traveled for two hours they would go 120 </li></ul><ul><li>miles but their speed would stay the same. </li></ul>
  8. 9. Projectiles… <ul><li>A projectile is any object that moves </li></ul><ul><li>Through the air or through space, </li></ul><ul><li>acted on only by gravity and any air </li></ul><ul><li>resistance if there is any. </li></ul>
  9. 10. Horizontal and Vertical Components… <ul><li>When you roll a ball freely along a level </li></ul><ul><li>surface, it moves at a constant velocity. This is </li></ul><ul><li>the same for the projectile. When no horizontal </li></ul><ul><li>force acts on the projectile, the horizontal </li></ul><ul><li>velocity remains constant. If you drop a ball </li></ul><ul><li>from a ledge there is a force due to gravity. A </li></ul><ul><li>projectile accelerates downward and its vertical </li></ul><ul><li>component of velocity changes with time. </li></ul>
  10. 11. Vectors Showing Both Horizontal and Vertical Components… <ul><li>The horizontal component is always the same </li></ul><ul><li>and only the vertical component changes. At </li></ul><ul><li>the top of the path the vertical component </li></ul><ul><li>shrinks to zero so the velocity there is the </li></ul><ul><li>same as the horizontal component in that case. </li></ul><ul><li>Everywhere else the magnitude of velocity is </li></ul><ul><li>greater. </li></ul>
  11. 12. Examples… <ul><li>Cannonball shot from a cannon </li></ul><ul><li>Stone thrown in the air </li></ul><ul><li>Ball rolling off the edge of a table </li></ul>
  12. 14. Upward Launched Projectiles… <ul><li>When a ball is thrown or a cannonball is </li></ul><ul><li>fired, it follows an upward launched </li></ul><ul><li>projectile. Gravity causes the ball to </li></ul><ul><li>follow a curved path until it finally hits the </li></ul><ul><li>ground. If gravity were not there the ball </li></ul><ul><li>would follow in a straight line instead. </li></ul>
  13. 16. Air Resistance… <ul><li>If air resistance isn’t there, a projectile will </li></ul><ul><li>rise to its maximum height in the same time </li></ul><ul><li>it takes to fall from that height to the ground. </li></ul><ul><li>this happens because of the constant effect </li></ul><ul><li>of gravity. The deceleration due to gravity </li></ul><ul><li>going up is the same as acceleration due to </li></ul><ul><li>gravity. </li></ul>